Not Applicable
Not Applicable
1. Field of the Invention
This invention pertains to passive energy dissipation systems in seismic applications, and more particularly to a method and apparatus for amplifying structural displacements for the driving of passive energy dampers.
2. Description of the Background Art
The use of damping devices on a structure to improve performance under shock, wind stress, vibration and so forth, is well known. Damping devices are typically connected to a rigid structure to receive the energy from the mechanical displacements to which the flexible building structure is subjected. The building is often referred to as a gravity frame and the rigid structure is often referred to as a reaction frame. A conventional damper for use in civil structures may be implemented with a large bore damper acting at very low pressure to minimize the rise time effects. However, this solution is often inefficient or impractical in that the damper can be difficult to package due to its large envelope, coupled with a high cost.
The use of less compressible fluid in the damper can reduce the size of a given damper yet these low compressibility fluids are not always practical as they are often toxic, flammable, or have less than favorable temperature characteristics or longevity.
Another attempt at improving the practicality of these seismic isolator makes use of a mechanism that combines a substantially braced column with a horizontal driving arm connected to the column and upper floor with hinge pins. An example of this mechanism being characterized by the xe2x80x9cDREAMYxe2x80x9d system described in the paper by Taylor, Douglas P. et al., Development and Testing of an Improved Fluid Damper Configuration for Structures Having High Rigidity, Taylor Devices, Inc., that can be found at www.taylordevices.com/techpaper2000.htm. In this configuration, vertically oriented dampers are connected at each end of the driving arm between the driver arm and the lower floor. Use of a lever in this manner increases the effective damper stroke, however, it may not be suitable for use in buildings or bridges because the entire mechanism is required to be extremely rigid to prevent the mechanism from flexing on the same level as the rise deflection of a direct acting damper, thus gaining no design improvement. In addition, utilizing a rigid mechanism necessitates hinge points that have very tight tolerances, while the mechanical links need to be large and heavy to prevent flexing under load. It will be appreciated that the external pin of the lever has to be free to move vertically to prevent the system from being locked in position. Furthermore, the close-fitting hinge points which allow in-plane response must not bind in the out-of-plane direction, and this requirement can readily drive up implementation costs.
Toggle braces have been developed to address certain limitations with lever-type damping mechanisms. Taylor et al., as well as U.S. Pat. No. 5,934,028 describe an approach that uses a toggle as a diagonal brace, with one end of the damper installed proximate the toggle pivot, and the opposite end attached to the building frame. With this approach, a relatively small lateral deflection in the building frame will cause a much larger deflection at the damper, due to the toggle mechanism multiplying deflections at the damper mounting point.
Therefore a need exists for an apparatus and method of increasing the amount of displacement energy which may be dissipated within a damper assembly of a given size, while not increasing implementation cost or reliability. The present invention satisfies those needs, as well as others, and overcomes the deficiencies with previously developed solutions.
The present invention generally comprises a displacement amplification mechanism which is capable of increasing the seismic energy dissipation of buildings and other similar flexible civil structures which are subject to displacement. Embodiments are described, by way of example, which utilize simple lever systems with arms of different lengths or with two concentric connected gears with different radius pinned at the center. The displacement amplifying apparatus of the invention is configured for use within a seismic isolator configured for attachment between a rigid structure and a flexible structure to dissipate seismic energy. It will be appreciated that the flexible structure, such as a civil structure, is often referred to as a gravity frame which under seismic, wind, vibration or other loading conditions becomes physically displaced and distorted. To provide seismic isolation, the energy from the movement of the gravity frame is dissipated in relation to a rigid reaction frame which typically comprises a rigid structure, such as an xe2x80x9cAxe2x80x9d-frame structure beneath the gravity frame. The reaction frame is typically not subject to the same inter story displacement forces as the gravity frame, but is utilized to extend a rigid base against which the energy may be dissipated. Seismic isolation is provided by the present invention by registering the motion associated with said inter story displacement which is amplified by the displacement amplifying apparatus whose output is received by a damping assembly. The inter story displacement applied to the damper will be amplified by the ratio of the length of the longer arm of the pivoting lever to that of the shorter arm, or by the ratio of diameter of the larger gear to the diameter of the smaller gear. In this way, the effective damper stroke is increased while, at the same time, the required amount of applied force at the damper mounting points is reduced. The invention can be used to amplify the relative inter story displacement that occurs during an earthquake in civil structures, and the resultant amplified displacement can then be used to dissipate energy by means of energy displacement devices such as a fluid viscous dampers (hydraulic dampers), friction dampers, viscous elastic dampers, and so forth.
In addition to amplifying structural displacements, the invention can provide altering the direction of the displacement, which can be beneficial in many situations, such as for meeting selected design constraints or in seismically retrofitting bridges. Furthermore, the invention allows for the use of viscous fluid dampers where the exponent of the damping coefficient is less than one, wherein damping efficiency is increased and more energy may be dissipated.
Additionally, damper beams could be constructed as integral units containing girders, displacement amplification devices according to the present invention, and dampers. These damper beams can be constructed and tested prior to installation into the structure. Further, xe2x80x9csuper dampersxe2x80x9d can be constructed using a plurality of displacement amplification devices integrated with one or more dampers according to the invention for significantly improving the energy dissipation capacity of a small damper. Utilization of a plurality of xe2x80x9csuper-damperxe2x80x9d devices rather than a few high-capacity dampers can provide cost-effective improvements of the seismic response of a structure. It will be appreciated that lever type and geared type amplification mechanisms may be mixed or interchanged to provide the desired seismic isolation. In accordance with a further aspect of the invention, a xe2x80x9cturbo damperxe2x80x9d can be constructed where, instead of amplifying the displacement and transferring the amplified displacement to a damper, the displacement is converted into rotational energy. The xe2x80x9cturbo damperxe2x80x9d is a rotating damper that integrates the functions of the mechanical displacement amplifier and the energy damper. The motion received by the xe2x80x9cturbo damperxe2x80x9d is converted to a rapid rotation of a propeller retained within a housing filled with viscous fluid.
Conventional seismic isolators such as the DREAMY system require the utilization of large components and are subject to possible problems with out-of-phase motion. A problem that is not present in the DREAMY system but exists in other systems is that the external pin of the lever has to be free to move vertically to prevent the system from being locked in position. In contrast, the present invention allows for the use of very short lever arms which are more rigid from a flexural point of view. Out of plane deformation can be solved by employing shear key plates. The last problem of allowing the vertical movement of the pin is solved within the present invention by utilizing flexible coupling point whose motion is constrained, this is exemplified by utilizing an elongated hole in the lever plate into which a coupling pin is retained. This pin-lever connection has the added benefit of allowing relative movement in the out-of-plane direction. The amount of movement being allowed being controlled by the configuration of the shear key plates. These features allow the present displacement amplification apparatus to be beneficially employed for dissipating seismic deformations and wind induced vibrations within large buildings and other structures.
An object of the invention is to increase energy dissipation within seismic isolators for use within civil structures and other large flexible structures.
Another object of the invention is to amplify the displacement of gravity frames in relation to a reaction frame whereby the damper assembly can be made more efficient and cost effective.
Another object of the invention is to provide a displacement amplification apparatus for use with gravity frames slidably engaged over an xe2x80x9cAxe2x80x9d-shaped brace of the reaction frame.
Another object of the invention is to provide a displacement amplification apparatus for use with gravity frames having a reaction frame that is not located proximal a portion of the gravity frame which is subject to displacement.
Another object of the invention is to provide a displacement amplifying apparatus that is capable of redirecting the displacement energy being dissipated. Another object of the invention is to provide a displacement amplifying apparatus that is capable of directing the amplified displacement of the civil structure to dampers attached at any of a number of locations, including the gravity frame, the reaction frame, or the base level.
Another object of the invention is to provide a displacement amplifying apparatus that is capable of directing the amplified displacement of the civil structure to dampers which are integrated within structural building elements.
Another object of the invention is to provide a displacement amplifying apparatus combined with a damper assembly, such that displacement forces are amplified and damped within a seismic isolator that has a lowered component count.
Another object of the invention is to provide a displacement amplifying apparatus for use in a seismic isolator which is both reliable and easily manufactured.
Further objects and advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon.